In the field of dentures a metal bar on implants is used to stabilize the denture in the mouth and to strengthen the denture structure to avoid breakage.
In the traditional denture manufacturing process an impression is made of a patient's implants and edentulous or partially edentulous ridges. The impression is used to construct a plaster model of the patient's edentulous ridges and implants. A metal bar is manufactured to fit exactly on the plaster model, and to align with the patient's implants according to the implant analogs in the plaster model. The metal bar is installed on the plaster model and the denture structure is then built around the bar in wax. Artificial teeth are placed in the wax resulting in a complete wax up of the denture with the bar incorporated on top of a plaster model. Traditionally, the next step is to investment cast the wax into acrylic resin.
For example, with reference to FIGS. 1A and 1B, a prior art system 100 is illustrated. A plaster model 102 is made of a patient's dentition. A bar 104 is installed on the plaster model 102 via implant analog interfaces 106. Wax mockup 108 is molded by hand and is mechanically wrapped around the bar 104. Artificial teeth 110 are installed. To finalize the denture, the system 100 is processed using investment casting, thereby causing wax mockup 108 to be replaced with acrylic denture material.
More recently, dentures have been made using CAD/CAM technology, such as by milling or 3D printing. With CAD/CAM technology, the denture is made directly without using wax and plaster models, thus no plaster model having implant analogues is available to align and position the bar. Consequently, a cavity must be cut in the denture and the bar fitted into the cavity. However, the bar is often complex in shape and difficult to precisely and securely fit in the denture. For example, small discrepancies will occur if the full shape of the bar is used for reference and registration.
Furthermore, even if such a plaster model were made to assist with aligning and positioning the bar in the cavity, the fitting of the denture onto the bar is difficult and often imprecise because it is difficult to preserve the proper registration of the bar with respect to the denture while they are mated and the bar disconnected from the plaster model, particularly if the model impedes access to the cavity in the denture. Moreover, the production of such a model introduces unwanted delay and expense.
Thus, there exists a need for an improved reference and registration system to position the supporting bar in a denture made using CAD/CAM technology.